Adaptive stabilization by output feedback is investigated for a class of nonlinear systems with parametric uncertainty in both state and output equations. Different from the existing work, the precise knowledge of the unknown parameter at the output, including its sign, is not required. The nonlinear system under consideration is assumed to be linear in the unmeasured states but does permit to be nonlinear with respect to the system output. To achieve global state regulation with stability, we employ the idea of K-filter and develop a universal-like output feedback control scheme using the Nussbaum gain. The proposed adaptive control strategy is then applied to tackle the problem of adaptive output tracking for the same class of uncertain nonlinear systems. Further extensions are also included, which address the adaptive output feedback control of a wider class of nonlinearly parametrized systems with output parametric uncertainty. (C) 2019 Elsevier Ltd. All rights reserved.